The present study on the green Anolis lizard (Anolis carolinensis) is designed as a further test of the hypothesis that the paleostriatum of reptiles, birds, and mammals plays a fundamental role in species-typical, communicative behavior. It deals specifically with the effect of lesions of the paleostriatum on the display behavior of the green lizard. Since the optic nerve is almost completely crossed, a lesion can be placed in one hemisphere and the animal's reactions to another lizard tested with a patch alternately placed on either eye. Lizards with lesions of the paleostriatum have shown statistically significant deficits in their aggressive display, whereas animals with lesions in other parts of the forebrain appear unaffected.